1. Field of the Invention
The present invention relates to a sealing and packaging device, wherein respective individual trays disposed at equidistant intervals in a column fashion, and band-shaped cover film for covering these respective trays, are moved and conveyed at the same speed on a conveyor line, the band-shaped cover film being welded successively to an edge flange portion of each tray.
2. Description of the Related Art
In what are commonly known as tray packaging machines, conventionally, there have existed devices having a structure wherein individual trays for respectively accommodating items to be packaged are disposed in a plurality of mould frames supported at equidistant intervals on an endless chain, these trays being conveyed along an endless path in a unified manner with the chain, while band-shaped cover film is fed over each of the trays, the film furthermore being welded to a flange portion at the edges of each tray, by means of a heating frame which descends from above. A merit is obtained in that the packaged item output by the packaging machine emphasizes the freshness of the food product accommodated in the tray, due to the transparency of the cover film which is attached horizontally to the upper face of each tray. However, if the packaged item is accommodated in the tray in a mounded fashion, then a problem arises in that the cover film covering same will be deformed into a bulging shape and will create a plurality of pleats.
U.S. Pat. No. 6,488,972 discloses a device which does not form pleats in the cover film. As illustrated in FIG. 16, U.S. Pat. No. 6,488,972 is a reference which relates to a device wherein an endless stretching frame 102 is pressed down about the perimeter of an item to be packaged 101, which is accommodated in a mounded fashion in a tray 100, and is pressed against the tray 100 while stretching the stretch film 103 against the resistance of the item to be packaged 101, in addition to which, the film 103 is welded to a flange on the perimeter edge of the tray by means of a heat sealer (sealing frame) disposed around the periphery of the stretching frame 102. The packaging machine described in this reference does have a merit in that pleating of the cover film is eliminated. However, when the stretch film 103 is stretched by the stretching frame 102, since the stretching frame 102 stretches the film 103 by means of friction, a plurality of wrinkles 104 are generated as a secondary effect in the portion of the film about the frame 102 which is not stretched. Consequently, this wrinkled portion becomes welded to the tray 100 by the heat sealer. Therefore, a problem arises in that the wrinkled portion 104 is liable to peel away from the tray 100, due to the elastic restoring force of the film that has been stretched.
The object of the present invention is to weld the film without forming wrinkles about the perimeter of the tray, when an item to be packaged which is accommodated in a mounded fashion in a tray is hermetically packaged by means of cover film. In other words, the present invention is suitable for the efficient hermetic packaging of block type items to be packaged, which stand up above a tray, without forming wrinkles in the cover film.
The present invention comprises: means for moving touch bars provided at equidistant intervals and spanning between endless chains in respective side positions, in a unified manner with the chains, and pushing and advancing respective trays along the upper face of a horizontal conveyance path, at equidistant intervals in a column fashion, by means of the respective touch bars; a general frame moving back and forth reciprocally in the same direction as the touch bars, in a cutaway region in an intermediate part of the conveyance path; bridge plates fixed to the general frame and moving back and forth reciprocally in a unified manner with the general frame, within the cutaway region at the same height as the face of the conveyance path; a lifting mechanism for moving a sealing base frame disposed surrounding the bridge plates, upwards and downwards, about the periphery of the bridge plates, in response to the reciprocal movement of the frame; sealers fixed to the general frame above the sealing base frame and having the same outline as the open edge of the tray supported on the sealing base; and a film conveyance mechanism for moving a band-shaped film between the sealers and the bridge plates, in the same direction as the touch bars; being composed in such a manner that, when the lifting mechanism performs an upward movement, the band-shaped film is pressed by the sealing base frame against film pushing elements disposed in isolated fashion about the periphery of the sealers, and, with further upward movement of the lifting mechanism, the band-shaped film is pressed against the sealers and welded by same at the open edge of the trays placed on the sealing base, while the band-shaped film is pushed upwards by a to-be-packaged item accommodated in the tray in a mounded fashion, and furthermore, the band-shaped film is pressed against endless blades surrounding the periphery of the sealers and is cut out in accordance with the outlines of the trays.
Moreover, the present invention comprises: means for moving touch bars provided at equidistant intervals and spanning between endless chains in respective side positions, in a unified manner with the chains, and pushing and advancing respective trays along the upper face of a horizontal conveyance path, at equidistant intervals in a column fashion, by means of the respective touch bars; a general frame provided in a fixed manner in a cutaway region in an intermediate part of the conveyance path; bridge plates provided in a fixed manner on the general frame within the cutaway region at the same height as the face of the conveyance path; a lifting mechanism for moving a sealing base frame disposed surrounding the bridge plates, upwards and downwards; sealers fixed to the general frame above the sealing base frame and having the same outline as the open edge of the trays supported on the sealing base; and a film conveyance mechanism for causing a band-shaped film to move between the sealers and the bridge plates, intermittently, in the same direction as the touch bars.
In U.S. Pat. No. 6,488,972, described above, since stretch film is pressed against a tray while being stretched by a stretching frame about a to-be-packaged item accommodated in a mounded fashion in the tray, a wrinkled section occurring at the periphery of the endless frame is welded to the tray by the heating frame, but in the present invention, since the portion to the inner side of pushing elements, where wrinkles are not liable to occur, is welded, occurrences such as peeling off of the welded section due to wrinkling are eliminated, and exposure of the packaged item to the air is prevented.